This application claims the priority of German patent document 197 05 278.9, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process and an arrangement for laser welding two metal sheets which overlap to form a flange seam and which are pressed together in the area of the flange seam, during the welding operation, the metal sheets and the laser beam being moved relative to one another and the welding being caused by a laser beam situated in the plane of the flange seam.
A process as well as an arrangement for the straight bead welding of container bodies by means of a laser beam are known from German Patent Document DE 36 30 889 A1. According to the process described therein, the sheet metal edges of workpieces being welded together are brought into a position such that together they form an acute angle. In order to produce a weld seam, a laser beam is then aimed into the opening formed by this acute angle. In this case, the arrangement has, among other things, several pressure rollers for fixating or for permitting the advancement of the metal sheet.
However, this process has the disadvantage that it can only produce a weld seam that is inaccurately positioned on the metal sheets to be welded together. It is even possible that the weld seam may fail to contact one of the metal sheets at all in one area.
German Patent Document DE 39 02 292 A1 describes a process for the additional welding of the connection area of lids, which are connected with a container body by folding, using a laser beam as well as an arrangement for carrying out such a process.
The insufficient positioning precision of the weld seam produced by the laser beam, in the case of this process and the connected arrangement is also a disadvantage.
For improving the positioning of the weld seam in the case of the known laser welding processes, seam tracking or search systems can be used. These, however, require high expenditures and correspondingly increase the cost of the welding arrangements.
For the welding of fuel tanks, roll seam welding, which belongs to the resistance welding processes, is known from the general state of the art.
In the past, fuel tanks were usually manufactured from steel. Lately, however, because of the general tendency in automobile manufacturing toward light-weight construction, these tanks have increasingly been made of aluminum. Roll seam welding is problematic and results in an increased energy requirement, in the case of aluminum. This is due to the higher thermal conductivity and the lower melting point of aluminum. Laser welding is thus used, in an attempt to solve this problem.
It is therefore an object of the invention to provide a process and an arrangement for laser welding by means of which the welding operation in general can be improved and the weld advancing speed can be increased. Furthermore, an accurate positioning of the weld seam with respect to the metal sheets to be welded together is to be achieved.
This and other objects and advantages are achieved according to the invention by spreading the metal sheet edges apart during the welding operation. In this manner, a geometry is provided such that, at any point in time of the welding operation, the laser beam can be aimed at a position that is precisely known in advance. As the result, a wedge-shaped weld seam is obtained which is precisely defined at any point in time.
In comparison to other welding processes, e.g., the known roll seam welding process, a significantly higher weld seam advancement speed is advantageously achievable. Moreover, the rejection rate is minimal because of the reduction of process defects.
Furthermore, by means of the process according to the invention, the flange width can be reduced. This contributes to a considerable saving of materials.
Additional possible advantageous developments of the invention are found in the subclaims and the embodiments described in principle in the following by means of the drawings.